As is known to those of skill in the art, Motor Control Centers (MCCs) can include cabinets or enclosures that hold multiple, typically modular, bucket assemblies or units of various sizes. See, e.g., U.S. Pat. No. 4,024,441, the contents of which are hereby incorporated by reference as if recited in full herein. Eaton Corporation has recently introduced a MCC product line with compact bucket assemblies that conveniently plug into a slot or space in an MCC cabinet. The product is sold under the product name, Freedom 2100 MCC. See also, U.S. Patent Application Publication Serial Number US2013/0077210, the contents of which are hereby incorporated by reference as if recited in full herein.
An MCC is a multi-compartment steel enclosure with a bus system to distribute electrical power from a common bus to a plurality of individual motor control units mountable within the compartments. The individual motor control center units are commonly referred to as “buckets” or “units” and are typically constructed to be removable modular units that have, or are installed behind, individual sealed doors on the motor control center enclosure. These units may contain various motor control and motor protection devices such as motor controllers, starters, contactor assemblies, overload relays, circuit breakers, motor circuit protectors, various disconnects, and similar devices for electric motors. The units connect to the common power bus of the motor control center and conduct supply power to a line side of the motor control devices for operation of motors and feeder circuits. MCCs are often used in factories and industrial facilities that utilize high power electrical motors, pumps, and other loads. MCCs and units therefore (the latter is also sometimes called “subunits”) are described in greater detail, for example, in commonly assigned U.S. Patent Application Publications 2009/0086414, 2008/0258667, 2008/0023211 and 2008/0022673, which are hereby incorporated herein by reference.
As shown in FIGS. 1A and 1B, MCCs can include units 10 with a circuit breaker 11 that can have an external accessory kit known as a “plug-in” arrangement. The plug-in arrangement can employ a stationary housing 15h (also known as a “plug-in block”) that is hard-wired to the bus and has forward facing sockets 15 on respective line and load sides that are aligned with and slidably receive and release plugs 17 mounted on the rear of a drawout cassette 20 holding the circuit breaker 11. The plug-in configurations can be incorporated into a drawout accessory, which is a plug-in arrangement with a racking mechanism accessible via a portal to engage a lever, crank or screw to move the breaker 11 to connect and withdrawn positions. FIG. 2 shows a MCC unit or bucket 10 that can be manually inserted into an empty cell or compartment of an MCC cabinet. Once secured with a unit interlock and the unit door closed, the plugs 17 can be racked in using a speed wrench which can be applied through a portal (such as portal 122 as shown in FIG. 11B). This can be described as a “FLASHGARD” configuration as it can provide additional operator safety and protection from an arc flash while inserting a bucket/unit when the cell door is securely closed.
FIGS. 3A and 3B illustrate an exemplary prior art schematic of a LG drawout breaker in an MCC as a vertical bus isolator. It is believed that some conventional MCC stab designs moved through about 1.75-2 inches of displacement from operational position to a disengaged (racked out) position of the stabs from the bus.